[llvm] [Object] Parsing and dumping of SFrame Frame Row Entries (PR #151301)

[James Henderson via llvm-commits]

================
@@ -100,6 +111,116 @@ uint64_t SFrameParser<E>::getAbsoluteStartAddress(
   return Result;
 }
 
+template <typename EndianT>
+static Error readArray(ArrayRef<uint8_t> Data, uint64_t Count, uint64_t &Offset,
+                       SmallVectorImpl<int32_t> &Vec) {
+  Expected<ArrayRef<EndianT>> RawArray =
+      getDataSliceAsArrayOf<EndianT>(Data, Offset, Count);
+  if (!RawArray)
+    return RawArray.takeError();
+  Offset += Count * sizeof(EndianT);
+  Vec.resize(Count);
+  llvm::copy(*RawArray, Vec.begin());
+  return Error::success();
+}
+
+template <typename T, endianness E>
+static Error readFRE(ArrayRef<uint8_t> Data, uint64_t &Offset,
+                     typename SFrameParser<E>::FrameRowEntry &FRE) {
+  Expected<sframe::FrameRowEntry<T, E>> RawFRE =
+      getDataSliceAs<sframe::FrameRowEntry<T, E>>(Data, Offset);
+  if (!RawFRE)
+    return RawFRE.takeError();
+
+  Offset += sizeof(*RawFRE);
+  FRE.StartAddress = RawFRE->StartAddress;
+  FRE.Info.Info = RawFRE->Info.Info;
+
+  switch (FRE.Info.getOffsetSize()) {
+  case sframe::FREOffset::B1:
+    return readArray<sframe::detail::packed<int8_t, E>>(
+        Data, FRE.Info.getOffsetCount(), Offset, FRE.Offsets);
+  case sframe::FREOffset::B2:
+    return readArray<sframe::detail::packed<int16_t, E>>(
+        Data, FRE.Info.getOffsetCount(), Offset, FRE.Offsets);
+  case sframe::FREOffset::B4:
+    return readArray<sframe::detail::packed<int32_t, E>>(
+        Data, FRE.Info.getOffsetCount(), Offset, FRE.Offsets);
+  default:
+    return createError("unsupported/unknown offset size");
+  }
+}
+
+template <endianness E> Error SFrameParser<E>::FallibleFREIterator::inc() {
+  if (++Idx == Size)
+    return Error::success();
+
+  switch (FREType) {
+  case sframe::FREType::Addr1:
+    return readFRE<uint8_t, E>(Data, Offset, FRE);
+  case sframe::FREType::Addr2:
+    return readFRE<uint16_t, E>(Data, Offset, FRE);
+  case sframe::FREType::Addr4:
+    return readFRE<uint32_t, E>(Data, Offset, FRE);
+  default:
+    return createError("invalid/unsupported FRE type");
+  }
+}
+
+template <endianness E>
+iterator_range<typename SFrameParser<E>::fre_iterator>
+SFrameParser<E>::fres(const sframe::FuncDescEntry<E> &FDE, Error &Err) const {
+  uint64_t Offset = getFREBase() + FDE.StartFREOff;
+  fre_iterator BeforeBegin = make_fallible_itr(
+      FallibleFREIterator(Data, FDE.getFREType(), -1, FDE.NumFREs, Offset),
+      Err);
+  fre_iterator End = make_fallible_end(
+      FallibleFREIterator(Data, FDE.getFREType(), FDE.NumFREs, FDE.NumFREs,
+                          /*Offset=*/0));
+  return {++BeforeBegin, End};
+}
+
+static std::optional<int32_t> getOffset(ArrayRef<int32_t> Offsets, size_t Idx) {
+  if (Offsets.size() > Idx)
+    return Offsets[Idx];
+  return std::nullopt;
+}
+
+template <endianness E>
+std::optional<int32_t>
+SFrameParser<E>::getCFAOffset(const FrameRowEntry &FRE) const {
+  return getOffset(FRE.Offsets, 0);
----------------
jh7370 wrote:

I'm a little concerned about this and the similar code in the following blocks, mostly because future ABIs/architectures won't necessarily have the same meanings for the different offsets. It's probably sufficient for now to add a comment or two highlighting that all supported ABIs use the specified offset.

https://github.com/llvm/llvm-project/pull/151301